The long-term objectives of the proposed studies are to understand the mechanisms underlying the expression of hemispheric specialization, particularly as it relates to language evolution and development. In the proposed studies, there are five mains aims. First, we aim to investigate whether microstructrual asymmetries are present in post-mortem brain tissue in specific regions of the cortex associated with language and speech functions as well as handedness. Post-mortem brains will collected and sections of tissue from specific regions of interest will be subjected to a variety of molecular and staining technqiues that allow for quantification of neuronal density and distribution. Second, whether microstructural asymmetries are associated with individual differences in gross anatomical asymmetries from comparable brain regions will be assessed in the proposed work. Post-mortem brains will be scanned using magnetic resonance imaging (MRI) and morphological regions of interest will be quantified and correlated with subsequent miscrostructural asymmetries measured from the same region. A third aim of the proposed studies is to assess whether individual differences in handedness are associated with microstructural asymmetries. Hand preferences for multiple measures will be assessed in a large group of subjects and upon natural death, the handedness of the subjects will be correlated with the morphological and microstructural asymmetries measured from the various brain regions of interest. Fourth, whether oro-facial asymmetries in the production of voluntary and involuntary sounds are differentially associated with neuroanatomical asymmetries from the language homolgs will be evaluted. Lastly, whether differences in orienting asymmetries to different classes of acoustic stimuli are present in primates will be assessed. Moreover, whether orienting asymmetries to different classes of stimuli are associated with variation in neuroanatomical asymmetries will be examined in the proposed studies. Overall, the proposed studies will provide invaluable data on the factors influencing the development and evolution of typical and atypical hemispheric specialization associated with communicative behavior as well as other motor, perceptual and cognitive functions.